1. Field of Invention
This invention relates to the bending of small diameter; heat deformable pipe or conduit such as plastic pipe and more particularly to field bending of such pipe or conduit.
2a. Technical Considerations
There has been an increase in the use of plastic conduit in the past several years. The conduit is generally used to protect electrical wiring. Due to the nature of its use, oftentimes the pipe must include a plurality of bends along its length. Factory degree bends can be bought and coupled together, but the additional costs may be prohibitive, especially if the conduit is to be used in a concealed area such as a concrete pour. As a result, the plastic conduit generally is bent free hand. However, with this method, the bends are not accurate or consistent. In addition, the conduit diameter may be altered along the bend from round to slightly oval so that wire pulling through the conduit in an electrical application can be difficult. Also, the general appearance of the plastic conduit bent free hand is poor, especially if it is used in exposed work, and it is very difficult to make the same repeated bend as is necessary when fabricating offset bent pipe. As used herein, an offset bent conduit is a conduit whose longitudinal axis is laterally shifted such that the longitudinal axis of a first portion of the conduit is parallel to but spaced from the longitudinal axis of a second portion of the conduit. The perpendicular distance between the spaced axes is the "offset" and the bends in the conduit are the "offset bends."
2b. Patents of Interest
Curtis U.S. Pat. No. 3,776,539 et al. discloses a plastic pipe bending jig having a plurality of operatively interconnected arms and pipe receiving clamps connected to the radial extremities of the arms. The clamps are radially and angularly adjustable to a desired radius and angle of curvature of the pipe. The jig is used by adjusting the clamps to define the desired pipe configuration, heating the pipe until pliable and placing the pipe in the clamps until the pipe hardens.
Miller U.S. Pat. No. 4,156,588 et al. discloses field forming of large diameter plastic pipes. The jig includes a two-piece spreader tube and a right and left hand U-shaped guide, each adjustable in width, angle and spacing. The guides are positioned along the spreader at a desired spacing and orientation relative to the spreader. In operation, the pipe section to be bent is heated and there placed on a flat surface. The guides are then lowered over the pipe so that each guide slides over a portion of the pipe on either side of the heated section.